2-layer Interference Coordination Framework Based on Graph Coloring Algorithm for A Cellular System with Distributed MU-MIMO

• Published in: IEEE transactions on vehicular technology Vol. 72; no. 3; pp. 1 - 12
• Main Authors: Ge, Chang, Xia, Sijie, Chen, Qiang, Adachi, Fumiyuki
• Format: Journal Article
• Language: English
• Published: New York IEEE 01.03.2023; The Institute of Electrical and Electronics Engineers, Inc. (IEEE)
• Subjects: Algorithms; Antenna arrays; Bandwidth; Color; computational geometry; Computer architecture; Coordination; distributed MU-MIMO; Frequency reuse; Graph coloring; graph coloring algorithm; Intercell interference; Interference; Interference coordination; Microprocessors; MIMO communication; O-RAN; ultra-dense cellular network
• ISSN: 0018-9545; 1939-9359
• DOI: 10.1109/TVT.2022.3219411

In this study, a cellular system with a large-scale distributed multi-user multi-input multi-output (MU-MIMO) is considered, in which a large number of distributed antennas are deployed spatially over each base station coverage area (cell) and user clusters are formed in each cell to perform cluster-wise distributed MU-MIMO in parallel. In such a cellular system, the intercell and intracell interferences coexist and limit the link capacity. In this study, a 2-layer interference coordination (IC) framework that can effectively mitigate the two types of interferences simultaneously is proposed. In the 1 st layer, the intercell IC is performed in a centralized manner by the non-real-time (non-RT) radio access network intelligent controller (RIC), and then in the 2 nd layer, under the condition of the results in the 1 st layer, intracell IC is done by each near-RT RICs in a decentralized manner. Furthermore, a restricted conditional graph coloring algorithm (RCGCA) suitable for this 2-layer IC framework is proposed. The proposed RCGCA is designed to be applied on a partial pre-colored graph, such that when it is applied in the 2-layer IC framework, it satisfies the requirement that the 2 nd layer coloring must be applied under the condition of the pre-coloring results of the 1 st layer. In addition, by restricting the total number of colors, the RCGCA can tradeoff between improving the capacity due to interference mitigation and degrading the capacity due to bandwidth partition, thereby maximizing the link capacity. We compare the link capacity achievable by the proposed 2-layer IC framework based on RCGCA with that achievable by the well-known fractional frequency reuse (FFR) scheme, no interference coordination case, fully centralized framework, and fully decentralized framework. Computer simulations confirm that our proposed 2-layer IC framework based on RCGCA can significantly improve the link capacity.